Syntax error Program to find index whose left and right elements sums are equal in Python

Program to find index whose left and right elements sums are equal in Python

Suppose we have a list of items called nums, we have to find the smallest index i such that the sum of the numbers which are present at the left of i is equal to the sum of numbers present at right of i. If we cannot find any such solution, return -1.

So, if the input is like nums = [8,2,3,6,5,2,5,9,1,2], then the output will be 4, because sum of elements that are left of index 4 is [8,2,3,6] = 19, and sum of elements that are present at right is [2,5,9,1,2] = 19 also.

To solve this, we will follow these steps −

  • r := sum of all elements present in nums

  • l := 0

  • for each index i and value x in nums, do

    • r := r - x

    • if r is same as l, then

      • return i

    • l := l + x

  • return -1

Example

Let us see the following implementation to get better understanding

def solve(nums):
   r = sum(nums)
   l = 0
   for i,x in enumerate(nums):
      r -= x
      if r == l:
         return i
      l += x
   return -1

nums = [8,2,3,6,5,2,5,9,1,2]
print(solve(nums))

Input

[8,2,3,6,5,2,5,9,1,2]

Output

4
Updated on: 2021-10-11T07:28:14+05:30

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